The invention relates to a process for reducing the nitric oxide emission during the combustion of solid fuels, particularly of hard coals, whereby reducing fuel is added to flue gases leaving a main combustion zone and is burned.
Nitric oxide emission of combustion plants operated with solid fuels may be influenced both by suitable control of the combustion process, so-called primary measures, and by the treatment of the flue gases leaving the combustor, so-called secondary measures.
While the primary measures are intended to reduce the generation of nitric oxides in the combustor, the secondary measures have the goal of removing the generated nitric oxides from the flue gases leaving the combustor.
Known secondary measures are e.g. the catalytic processes for the selective separation of nitric oxides. But these processes are complex and expensive. The disposal of the used or loaded catalysts also causes problems.
Another, comparatively simple, possibility for reducing nitric oxide emission consists of mixing an additional reducing fuel to the flue gases leaving the main combustion zone of a combustor and to burn it in a so-called reduction zone. But this measure by itself is often not sufficient for keeping within the limits of legally prescribed emission limits for nitric oxides so that secondary measures such as e.g. catalytic denitrogenation as a rule cannot be foregone.